1. Field of the Invention
The present invention relates to an I/O cell capable of switching an output current.
2. Description of the Related Art
In recent years, an I/O cell is used for an input/output of an LSI. It is required for the I/O cell, as an interface between two circuit blocks, which operate with different power-supply voltages, to be capable of switching output drive capabilities (output voltages). Here, as a method for switching output voltages, a method is known in which ON/OFF states of output transistors of different channels (Pch, Nch) are switched.
However, when switching the output transistors, if both channel transistors (Tr) are ON, then, a through current flows.
With respect to the above, it is proposed in Patent Document 1 that, in order to prevent destruction of output transistors due to the increased through current caused by increased output power, the through current is reduced by connecting low-output-current transistors in parallel, and by switching simultaneously a high-output-current transistor and the low-output-current transistors, and thus, causing the through current to flow in the low-output-current transistors.
Further, it is proposed to adjust circuit constants of a latch circuit (pre-buffer) in order to create a period in which both a Pch output transistor and a Nch output transistor are OFF.